Synchronizing device



Dec. 9, 1952 H. ERNYEI SYNCHRONIZING'DEVICE 2 SHEETS-SHEET 1 Filed Jan.5, 1949 INVENTUR RT ERNYB HERBE i ATTUR H. E RNYEI SYNCHRONIZING DEVICEDec. 9, 1952 2 SHEETSSHEET 2 Filed Jan. 5, 1949 m R m 7 Pm m T m m B m Hm 3 I T um fi MM p addd J n B .ZVL 1-} A z Z ATTORNEYS Patented Dec. 9,1952 SYN ZHRONIZING DEVICE Herbert Ernyei, Paris, France, assignor toSociety La. Radio-Industrie, S. A., Paris, France, a society of FranceApplication January 5, 1949, Serial No. 69,322 In France July 5, 1948 3Claims. 1

The present invention relates to scanning devices for televisionreceivers.

Its chief object is to provide a device of this kind which is betteradapted to meet the requirements of practice than those used for thesame purpose up to this time, and in particular a device such thatrelaxation oscillations cannot be too easily started by signals orimpulses other than television synchronizing pulses received from thetelevision transmitted, but that, on the contrary, the scanning circuitsoscillate freely on their natural frequency in the absence of receptionof synchronizing pulses.

According to an essential feature of my invention, in a device of theabove mentioned kind,

' controlled by at least one relaxation oscillation generator includingmeans for blocking the output thereof and means for periodicallyneutralizing said blocking means, I provide a device for applying tosaid blocking means a negative bias such that, outside of the times ofreception of synchronizing pulses from the television transmitter, whichneutralize said blocking means, the voltage applied to said lastmentioned means remains substantially lower than the value for whichsaid blocking means is neutralized, the negative bias voltage necessaryfor this purpose being supplied in response to the reception of carrierwaves from the transmitter, whereby, in the absence of such carrierwaves, any bias ceases to be applied and the relaxation device startsoscillating freely.

Preferred embodiments of the present invention will be hereinafterdescribed with reference v eration of the grid of the output tube ofthis last mentioned multivibrator;

Fig. 6 is a diagram showing a method of filtering the carrier waves thatare received to collect therefrom a negative bias voltage.

Among the devices capable of producing relaxation oscillations fortelevision receiver scanning devices, it is known to use a cathodecoupling multivibrator such as shown by Fig. 1. It is known that such amultivibrator includes chiefly two electronic tubes I and 2 coupled onthe one hand through a common cathode resistor 3 and on the other handthrough a capacitor 4 inserted between the anode of tube l and the gridof tube 2. The multivibrator further includes a capacitor 5 and aresistor 6 for biasing the grid of tube I, a rheostat l for biasing thegrid of tube 2, a fixed resistor 8 and a variable resistor 9 in therespective plate circuits of tubes I and 2 and a capacitor ID in theplate circuit of tube 2. II represents the various parasitic capacities.

I will first summarily explain how relaxation oscillations take place insuch a multivibrator. If I take as starting point the time a when tube 2is blocked by the negative bias on its grid, condenser lfl first getscharged. Tube l is conductive and maintains a constant potential on itsplate. However its capacitor 4 discharges through resistor 1 so that thebias on the grid of tube 2 decreases gradually until, at time b, thistube becomes conductive, which causes capacitor [0 to discharge. Tube 1is then quickly blocked due to the rise of the cathode potential createdin resistor 3. This blocking causes the plate potential to rise quickly.This variation is transmitted to the grid of tube 2 and accelerates thedischarging of capacitor [0. Near the end of the discharge of thiscapacitor, current flow is slowed down in tube 2. Consequently, theoathode potential of tube l becomes more negative until time 0 when thistube again becomes conductive, which has for its effect to apply anegative bias on the grid of tube 2 and to block it. The relaxationcycle is then complete and a new cycle starts.

Fig. 2 shows waveforms of the voltage V in various portions of the abovedescribed multivibrator. Waveform I relates to the plate n of tube 1 andwaveform II to the grid 1 of this tube. Waveform III relates to theplate 112 of tube 2 and waveform IV to the grid Q2 of this tube. It isknown that capacitor H) can be started discharging at a time b earlierthan I) if a negative voltage impulse is sent at this time b to the gridof tube I. Such an impulse is shown in waveform II and consistspractically in the synchronizing pulse of the television transmis-51011.

It is therefore visible that such a relaxation generator has a naturalfrequency, which on the other hand can be synchronized to a slightly 3higher frequency, determined by synchronizing pulses.

However, such a generator has drawbacks which result chiefly from a lackof rigorous determination of the time at which oscillations are started.Three main causes can modify this time: first, variations in the directvoltage; secondly, the existence of parasitic oscillations at about thetime when capacitor 4 is nearing the end of its discharge, which mayhave for its effect prematurely to start discharge of capacitor Iii;thirdly, anomalies in the feed voltages (for instance a superposition ofthe network voltage to the high frequency voltage), which may modify theslope of curve V or VI (Fig. 3) which represents the rid voltage of tube2, and therefore involve an uncertainty as to the time 751 or its whenthe multivibrator is released into oscillation, this time beingdetermined by the intersection of the release level l2 with curves VIIand VIII, which represent a synchronizing pulse.

It has been already endeavored to obviate the drawbacks inherent in theabove described device. Among the solutions that were .proposed, can bementioned in particular that which consists in replacing themultivibrator by a single tube connected like tube 2 and in whichperiodical discharges of condenser 58 are produced by a synchronizingpulse of positive value applied to the grid of this tube. This solutionhas a serious drawback: in the absence of synchronizing pulses, i. e.after the end of the transmission, scanning of the receiver tube ceasesand the fluorescent layer of this tube risks being deteriorated bycontact of the spot which then remains stationary.

The object of the present invention is to remedy the drawbacks offered bthese various relaxation oscillation generators. According to thisinvention, in a generator in which each relaxation oscillation isreleased by the neutralizing of an electronic blocking device insertedin the circuit of the generator, a negative bias is applied to thisblocking device so that, in the course of normal operation, its basevoltage remains substantially below the neutralization voltage of thisdevice, the negative voltage necessary for producing this bias beingproduced in response to the reception of carrier waves from thetelevision receiver, so that, in the absence of such carrier waves, anybias ceases to be applied on the blocking device and the relaxationdevice starts oscillatin freely.

The invention can apply to any relaxation device. By way of example, ithas been hereinafter supposed that it is applied to a multir vibrator ofthe kind above described, but it should be understood that it might aswell be applied to other generators, and for instance to blockedoscillators.

Fig. 4 shows a multivibrator made according to the invention. It will beseen that it differs from that of Fig. 1 in that a negative bias isapplied to rheostat l by means of a device la which is to bemoreexplicitly referred to hereinafter. On the other hand, it isadvantageous greatly to reduce the time constant of the circuitincluding capacitor 4 and rheostat I, so that the curve representing thegrid voltage Vgz of tube 2 with respect to time has an appearancesimilar to that represented in Fig. 5.

- It will be seen that the working of the multivibrator thus modified isquite different from that above described: On the one hand, tube l actsonly, in this case, as a negative pulse 'reverser, to transiormit into apositive pulse applied tothe grid of tube 2, and, on the other hand,when a negative bias is applied to rheostat l, discharge of capacitor l0takes place only in response to a synchronizing pulse. In order to havethe system oscillating freely in the absence of such pulses, thenegative bias must no longer be applied to rheostat in the absence ofthese pulses, i. e. when there is no transmission. This bias voltagemust therefore be created by means of a device la controlled by thecarrier waves that are received.

This negative bias voltage can be obtained as wellfrom the picturecarrier wave as from the sound carrier wave, or again through othermeans, in particular those for obtaining in television an automaticvolume control or antifading voltage. When thus making use of thepicture carrier wave, the negative voltage that is obtained should befiltered in a circuit having a very high time constant, in order toeliminate the effects of variations of the direct component of thepicture carrier waves.

Fig. 6 shows an advantageous arrangement which permits of thus obtaininga negative bias voltage from the picture carrier wave arriving at H. Inthis arrangement, the intermediate frequency transformer I in has itsoutput connected with diode l2 through a capacitor 13, in shunt withresistor Id on which is obtained the videofrequency current, with itsdirect component, which current is collected at [5 in the receiverdevice. This component is separated from the modulation current and itsvariations are slowed down in circuit i%ll, which has a very high timeconstant (of the order of some seconds) The negative bias voltage thusobtained is collected on rheostat 'i belonging to the relaxationoscillation generator (8 according to the invention.

Such a television receiver scanning device has many advantages, and inparticular that of a high precision in operation, without risk ofdeterioration of the receiver fluorescent screen in case of stopping ofthe transmission.

In a general manner, while I have, in the above description, disclosedwhat I deem to be practical and eflicient embodiments of my invention,it should be well understood that I do not wish to be limited thereto asthere might be changes made in the arrangement, disposition and form ofthe parts without departing from the principle of the present inventionas comprehended within the scope of the accompanying claims.

What I claim is:

1. For use in connection with a television transmitter capable ofsending out a carrier wave and synchronizing pulses, a televisionreceiver whichcomprises, in combination, a self-oscil latory relaxationoscillation generator arranged to be blocked in response to theapplication of a given bias voltage on an element thereof, and means forsupplying said bias voltage in response to reception of said carrierwave, said means having its output connected with said element, saidrelaxation oscillation generator including means responsive to saidsynchronizing pulses for neutralizing the action of said blocking meansupon every reception of a synchronizing pulse.

2. For use in connection with a television transmitter capable ofsending out a picture carrier wave and synchronizing pulses, atelevision receiver which comprises, in combination, a selfoscillatoryrelaxation oscillation generator arranged to be blocked in response tothe application of a negative bias voltage on an element thereof, andmeans for supplying said bias voltage in response to reception of saidcarrier wave; said means having its output connected with said element,said relaxation oscillation generfator includin'g means responsive tosaid synchrofnizingpulses for neutralizing the action of said" blockingmeans upon every reception of a' synchronizing pulse.

3. For use in connection with a television transmitter' capable ofsending out a carrier wave and 10 synchronizing pulses, a televisionreceiver which comprises, in combination, a self-oscillatory relaxationoscillation generator arranged to be blocked in response to theapplication of a given; bias voltage on an element thereof, a detectorstage, and a high time constant filter circuit in cluding a resistorinserted between the output 'of i said detector stage and said elementand an earthed capacitor in shunt with said resistance,

for supplying such bias voltage to said element when said carrier waveis being transmitted, said relaxation oscillation generator includingmeans responsive to said synchronizing pulses for neu- 'tralizing theaction of said blocking means upon every reception of a synchronizingpulse.

HERBERT ERNYEI.

REFERENCES CITED The following references "are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,141,343 Campbell Dec. 27, 19337 2,231,792 Bingley Feb. 11, 1941 2,338,395 Bartelink Jan. 4, 1944"2,431,577 Moore Nov. 25, 1947 2,511,146 Beste June 13, 1950

